This month, I’ll
describe a nifty
pocket-sized USB
spectrum analyzer and
show its pros and cons
through some measurements
on an ATSC signal,
out after the mask
filter and with some popular
TV antennas.

TRIARCHY TSA5G35 USB
SPECTRUM ANALYZER
A few months ago in RF Report, I described
a USB spectrum analyzer the size
of a small USB TV tuner stick. The device
isn’t much larger than a USB flash drive
and looks similar to a USB TV tuner stick
except for its SMA connector. I decided to
check it out.

The device has two separate bands—1
MHz to 850 MHz and 850 MHz to 5.35
GHz. Frequency spans are fixed and range
from 1 MHz to 1,000 MHz. Fig. 1 shows the
only data available besides what’s seen on
frequency/amplitude display graticule.

Unfortunately, there is no option to
measure channel power, which makes accurate
DTV signal-level measurements difficult.
This appears to be a software, not a
hardware, limitation, so perhaps a future
version will support it. Sweep is normally
2 seconds and burst mode allows it to
capture short pulses to accurately display
spread spectrum and frequency hopping
signals such as Bluetooth and Wi-Fi.

Fig. 1: Triarchy measurement

(Click to Enlarge)

The input level range is –110 dBm to
+30 dBm using the provided SMA attenuator.
The device has a maximum usable display
range of about 80 dB. Its noise floor
is –115 dBm with a 5 MHz span at a –60
dB reference level at 1 GHz. Wider spans
or different reference level settings will increase
the noise floor and limit the usable
dynamic range.

I hooked the TSA5G35 up to the output
of a Channel 30 mask filter to see if the
device might be useful in checking shoulder
level. Fig. 2 shows the display from the
TSA5G35 software. You can see the signal
coupled into the Channel 30 antenna
from a Channel 31 transmitter on the same
tower. This was a clean transmitter—FCC
mask shoulder levels were around 50 dB
down—so only a hint of the shoulder is
visible.

While it can provide a quick check of
transmitter performance, this miniature
spectrum analyzer is more useful for seeing
what signals are present and their relative
amplitude. The wide span and max hold
make it ideal for tracking down interference.
I used it to compare three popular antennas,
the Winegard FreeVision FV-HD30
and Mohu’s Leaf Plus and Leaf Ultimate.

Fig. 2: 8VSB spectrum display

(Click to Enlarge)

COMPARISON OF THREE
POPULAR ANTENNAS
The FV-HD30 can be used indoors
or outdoors and unlike many indoor antennas
offers excellent performance on
high-VHF channels. Even though it isn’t
amplified, in Los Angeles it worked better
than both my amplified Terk HDTVa log-periodic/rabbit ears and Winegard SS-
3000. I had been carrying the Mohu Leaf
Plus in my laptop bag, but the Ultimate
uses a USB powered bias-tee power injector
that is not tethered to the antenna. It
can be placed next to the tuner or laptop
making it much easier to set up. It isn’t
necessary to run a separate power cable
to the antenna.

I tested these three antennas by placing
them one by one against the same
spot on an interior wall roughly facing
Mount Wilson. The Los Angeles transmitter
sites were obstructed by three walls
and the Santa Monica Freeway. To evaluate
antenna performance, I did plots with a
500 MHz span centered on 300 MHz (50–
550 MHz) and 600 MHz (450–850 MHz)
plus 100 MHz span plots centered on 195
MHz (145–245 MHz) and 605 MHz (555–
655 MHz) for each antenna. You can view
all of the plots at www.xmtr.com/RF239.

While the antennas were all tested in
the same location, you’ll see some variation
in the response of individual channels
due to reflections from vehicles on the adjacent
freeway.

Fig. 3 shows the 500 MHz plot centered
at 600 MHz from the Leaf Ultimate. At UHF,
all three antennas provided mid-band signals
approximately 30 dB above the analyzer
noise floor. The Mohu Leaf Ultimate
and the FV-HD30 provided slightly better
high-UHF signals relative to the noise floor
than the Mohu Leaf Plus.

Fig. 3: Mohu Ultimate UHF band spectrum

(Click to Enlarge)

The amplifier in the Ultimate has about
10 dB more gain and there does appear to
be some filtering of the frequencies above
the TV band, with 700 MHz LTE downlink
signals about 11 dB below the highest UHF
TV signals. The LTE downlink signals were
only 6 dB below the highest UHF TV signals
on the other two antennas.

Mid-band UHF output level from the antennas
on Channel 36 was about –69 dBm
for the unamplified FV-HD30, –67 dBm
for the Leaf Plus and –50 dBm for the Leaf
Ultimate. The specifications on the amplifier
used in the Ultimate are: minimum 15
dB gain, <2 dB noise figure, and an output
IP3 of 37.5 dBm. With this much amplification
that’s important and given the performance
of some tuners, an unamplified
antenna may do better in strong signal environments.

I did not check low VHF performance.
The FV-HD30 picked up Channel 9 at
–68 dBm, with a spectrum analyzer noise
floor of –100 dBm. The Leaf Plus had
–52 dBm on Channel 9 with a –80 dBm
analyzer noise floor. Channel 9 came in
at –48 dBm, also with a –80 dBm noise
floor, on the Leaf Ultimate. Channel 7 signal
levels were about the same as Channel
9. I didn’t see any indication of FM
band filtering on these devices, although
it appeared the Leaf Plus had a lower FM
signal level when compared to high-VHF
channels.

As you can see in the plots, the software
is poor. For example, the graticule marks
don’t line up with the scale. I hope Triarchy
or a third-party developer takes advantage
of capability of the TSA5G35 hardware and
updates the software. The software can
send data over an IP connection for remote
monitoring so it should be possible to grab
it and post-process it to add measurements
such as channel power. Another project to
add to the list!

The FAA’s current rules and proposed ban on flight over people, requirement of visual line of sight and restriction on nighttime flying, effectively prohibit broadcasters from using UAS for newsgathering. ~ WMUR-TV General Manager Jeff Bartlett